The function of the compression stand is to enable the lid to be pressed against the body of the can with greater or lesser force during the closure stage proper during which the edge of the lid is rolled over the edge of the body of the can and is then flattened out in order to obtain a sealed connection by peripheral crimping. The pressure exerted on the lid has a determining influence on the quality of the crimping roll formed around the edge of the lid. For any given type of can, said pressure should remain at a well-determined constant value: pressure that is too low or too high leads to faulty crimping.
In the mechanism described above, the compression stand bears, via the spring, against the second above-mentioned element which serves as a control member, the assembly performing reciprocating motion that is performed at an increasing rate with an increasing crimping throughput.
When the rate is low, inertia phenomena are small and the compression stand tracks the displacements of the control member accurately, with the spring remaining is a substantially constant state.
As the rate increases, the inertia of the compression stand and of the first element to which it is fixed subjects the spring to force on each stroke of the assembly towards the can to be closed. Since the spring exerts the pressure required for crimping properly only when stabilized, it will be understood that the degree of compression departs from the desired value and that the faster the rate the greater the departure, particularly if the cans to be closed are of a type that requires only a small amount of compression force, and thus a spring that is relatively weak (as applies, for example, to thin-walled cans made of light alloy).
Incompatibility thus appears to exist between closing food cans at a high rate and obtaining low compression force thereon during the crimping operation.